732 THE POPULAR SCIENCE MONTHLY. 



was really f urnisliing the observer with a series of natural experi- 

 ments on man in the form of disease. The physiologist removed 

 a piece of the brain and watched the loss of sight or hearing, or 

 the loss of motion which ensued. The physician, on the other 

 hand, watches the same kind of loss of sight and hearing, or of 

 motion, in his patient, and may perhaps conclude that here too a 

 loss of brain-tissue is the cause. And this conclusion was con- 

 firmed by further observation. Perhaps this may be made a little 

 clearer if we add a fact or two regarding the way in which these 

 experiments of nature are conducted. The blood which is sent to 

 the brain at every throb of the heart goes up in a set of tubes, 

 which give off side branches, like the system of water-pipes which 

 connect your basins with the reservoir. Each tube gets smaller as 

 its branches are given off, until at the end, instead of one large 

 pipe, there is an innumerable series of little end pipes, each throw- 

 out its little stream. 



Let us picture to ourselves the water-pipe system of a town set 

 up on a frame aboveground, with the great main, the street 

 mains, the house pipes, and the little pipes all over the houses, all 

 in view, and we will have a sort of conception of the brain's vessels 

 and its blood-supply. Now, it is easy to see that, if a stick or a 

 mass of leaves start out from the reservoir into a main, they will 

 go on and on till they reach a pipe too small to allow them to 

 pass, and there they will lodge. If the stick gets into one's house 

 pipe, one's entire house will be cut off from the water-supply ; if 

 the mass of leaves breaks up, a few particles may come in and 

 plug up a pipe to one only of the basins. But in either case the 

 basin will be as useless for washing purposes as if there were no 

 reservoir at all. Now, something very similar to this occurs in 

 disease. Little plugs sometimes come up to the brain from the 

 heart in the blood, and lodge in the little vessels which conduct 

 the blood to various parts of the brain ; and when the part of the 

 brain is thus cut off from its supply of nutrition, it gradually 

 withers up and ceases to act. 



But when it ceases to act, a loss of some one sense results, just 

 as in the dog when a part of the brain was cut out a loss of some 

 sense occurred. When these facts were studied in this way, it soon 

 became evident that in some persons it was the sight, in others the 

 hearing, in others some other sense, in others still the power of 

 movement which was lost ; and further study showed that the vary- 

 ing effect depended upon which part of the brain was deprived of 

 nutrition and was withered, just as in the dogs the location of the 

 part removed determined which sensation was destroyed ; so that a 

 striking parallel between the results of experiment and the results 

 of disease can be drawn ; and thus the conclusion is arrived at that 

 what is true of animals is true of man, that in man as well as in 



